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SU‐E‐T‐709: Spatial Resolution Requirements for Fragment Identification in a Carbon Ion Spread Out Bragg Peak
Author(s) -
McBeth R,
Borak T
Publication year - 2015
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4925073
Subject(s) - sobp , pixel , bragg peak , imaging phantom , image resolution , ion , physics , monte carlo method , optics , detector , materials science , beam (structure) , nuclear medicine , mathematics , statistics , medicine , quantum mechanics
Purpose: To determine spatial resolution for detectors used to identify charged fragments in a carbon ion therapy spread out Bragg peak. Methods: The Geant4 Monte Carlo toolkit was used to simulate a 2 × 2 cm 2 broad beam of carbon ions incident on a 30 × 30 × 12 cm 3 water phantom. The carbon ion energies ranged from 165 MeV/n to 220 MeV/n and intensities were selected in order to simulate a SOBP extending from 6 to 10 cm in depth. Scoring of secondary fragments was performed for different pixel sizes at 3 depths in water. The analysis was designed to identify situations where two or more fragments intercept a pixel coincidently. Results: Initial results show that increased depths in the phantom require smaller pixel sizes due to increases in fragment population. At a pixel size of 1 × 1 cm 2 , a detector pixel was intercepted by two or more particles 16%, 14% and 30% percent of the time at depths of 6, 8 and 10 cm respectively. The probability of coincident hits decreases with smaller pixel size. At a pixel size of 0.05 × 0.05 cm 2 a detector pixel was intercepted by two or more particles 0.7%, 0.9%, and 2% of the time at depths of 6, 8 and 10 cm respectively. Conclusion: Accurate characterization of carbon ion beams requires the consideration of secondary charged particles that have different radiobiological effectiveness. A method for accurate identification in a clinical setting could lead to improved models for treatment planning. This work investigated the spatial resolution requirements for a detector that could be used to perform secondary fragment identification in a spread out Bragg peak. These preliminary results show that detectors with pixel size on the order of 0.5 × 0.5 mm 2 may be sufficient. This work was supported through research grant NNX13AD19G for Early Stage Innovations (ESI) administered through the NASA Space Technology Research Grants Program. No conflict of interest.